Electrical regulator system



Sept. 21, 1943. T. c. -ENNOX 2330,0633

ELECTRICAL IEGULATOR SYSTEM Filed March 28, 1942 Fi .l. 2

F I l U flwuurm 5561/01 70/? A 5 REGULATOR A Q I Y [0/222 X, FM? Inventor:

Thomas GLer'mox,

b y His Attorney.

Patented Sept. 21, 1943 UNITED STATES PATENT OFFICE g 2,330,063 ELECTRICAL anoULA'roa sysrm Thomas C. Lennon, Pittsfleld, Masa, assignor to General Electric Company, a corporation 0 New York Application March 28, 1942, Serial No. 436,688

8 Claims. (01. 171-419) I latively, or by moving the core or a part thereof with respect to the windings, or by core saturation,with or without magnetic shunts. Another class depends upon varying the relative number of effective turns of the windings; that is to say, the relative number of winding turns in the respective circuits of the transformer, as by the use of tap-changing switches or their equivalent.

When these ratio varying means are controlled automatically in response to a variable quantity, such as voltage. the combination is known as an automatic variable ratio transformer type regulator.

ation in this condition. At first thought it might means in the form of small autotransformers or reactors through which the regulating transformers are connected in parallel circuit relation. In addition to substantially eliminating harmful circulating currents, while at the same time having no substantial eflect on the transformer load currents, these devices permit stable operation of parallel regulators when they are controlled respectively by their own automatic control means. This in turn results in closer regulation in that the number of separate regulating steps for the regulated circuit will be increased substantlally.

An object of the invention is to provide a new andimproved electrical regulator system.

Another object of the invention is to provide an improved system of parallel operation of variable ratio transformer type regulators.

A further object of the invention is to provide an improved system of parallel operation of step voltage regulators which results in stable operation without the use of any auxiliary interconseem that this dimculty could easily be solved by interconnecting the ratio varying means of the transformers to be paralleled so that it would be impossible to vary the ratio of one transformer without equally varying the ratios of the others. However, this involves either control interconnections or else mechanical interconnections between the transformers which are expensive and not always practical, as when the regulating transformers are not located physically very close together. Furthermore, many regulating transformers of the tap-changing type have. spring driven actuating mechanisms for causing snap action of the ratio adjusting tap-changing switches and even if these mechanisms are driven by the same motor or power shaft it is practically impossible to have the switches of both regulators snap from one position to the other at exactly the same instant.

In accordance with this invention I provide a novel and simple paralleling system which is characterized by the use of auxiliary inductive nection between the regulators other than the necessary paralleling connections.

The invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing Fig. 1 illustrates diagrammatically an embodiment of the invention as applied to the paralleling of two equal-size automaticallycontrolled single-phase variable-ratio autotransformers of the tap-changing type, otherwise known as step regulators, Fig. 2 is a modification in which two unequal-size three-phase regulators are paralleled and Fig. 3 is another modification in which three three-phase variable ratio regulating transformers are paralleled. I

Referring now to the drawing and more particularly to Fig. 1, the system comprises a singlephase supply circuit having a conductor I and a single-phase constant voltage load circuit having a conductor 2. These circuits have a common retum conductor indicated by the ground 3.

Connected effectively in parallel in the circuit are a pair of equal-size automatic step voltage regulators 4 and 4'. These consist respectively of multi-tapped windings 5 and 5. The taps are connected respectively to tap-changing switches 6 and 6 which are driven respectively by motors 'l and 1' under the control of primary voltage sensitive relays 8 and 8' which are energized respectively by auxiliary windings 9 and 9 which are excited by transformer action from the main autotransformer windings 5 and 5'. The conductor i is electrically connected directly to the movable contacts of the switches 8 and 8'. These movable contacts constitute the input terminals of the regulators. The output terminals of the regulators are located at an intermediate point in the autotransformer windings, preferably at the middle one of the taps for in this way the regulator may be made selectively to raise or lower the voltage. of the load circuit 2'. These output terminals are therefore shown at It! and I and they are connected respectively to the terminals of an inductive device in the form of an autotransiormer or mid-tapped reactor H, the midpoint of which is connected to the conductor 2.

The remaining terminals of the autotransformer regulators are connected to ground and constitute their common terminals.

The operation of Fig. 1 is as follows: It will be observed that the tap-changing switches 8 and 6' connect the input circuit I directly to the middle one of the taps in the autotransiormer windings so that in eflect the input and output assopos ly low magnetizing current of the winding H. I The load current will continue to divide substantially ehually between the two regulators because of the neutralizing action of the load current in the two halves of the winding. However, as the winding H constitutes an autotransformer the voltage of its mid-terminal will be half way betweenthe voltages of the output terminals in and It so that the voltage of the output circuit will be the average of the output voltages of the two regulators.

terminals of the regulators are directly-connect;

ed by the tap-changing switches. Consequently. the regulators neither raise nor lower the voltage and they are therefore in what is usually called their neutral positions in which they both have a 1:1 voltage ratio. They have substantially zero impedance in this position. As the two halves of the winding II also have equal impedance and as the currents through the two regulators will produce opposing .magnetomotive forces in the halves of the winding i I, this winding offers substantially zero reactance to the flow of equal load currents through the regulators and consequently they operate in parallel and divide the total current equally which is as it should be because the regulators have equal ratings.

Assume now that the voltage of the circuit 2 falls slightly below normal, that is to say, slightly below the value for which the relays 8 and 8' are adjusted to balance. If'both relays have identical settings and identical characteristics they will respond equally so that if the fall in voltage is sufflcient they will both close their respective raise contacts thereby causing simultaneous operation of the motors l and 1' and if the driving mechanisms betweenthese motors and the tap switches have identical time constants the switches will move clockwise in unison one step thereby reducing the eflective number of turns of the primary windings of the regulators withrespect to their secondary windings so as to raise the voltage of the load circuit. Ii this restores the voltage of the load circuit to normal the relays will reopen their contacts and stop the operation of the tap-changing means. As the ratios of both regulators have been changed the same amount there will be no unbalanced voltage tending to circulate current The automatic control means of'theregulators are stable for this condition of operation because they respond only to the output voltages oi their respective regulators so that the primary relay 8 is not ailected by the tap-change produced in the regulator 4' even though the voltage of the load circuit has changed. The reason the primary relays respond only to the output voltages of their respective regulators is that the turn ratios between the secondary windings of the main autotransformers and their respective auxiliary windings are fixed and are not altered by operatfin oi the tap-changing switches.

As the tap change produced in the regulator 4' raises its output voltage but does not raise the output voltage of the regulator 4. the primary relay 8' will be nearer its voltage lowering position than will the primary relay 8 so that if the voltage of the load circuit continues to fall the relay 8 will close its raise contacts before the;

relay 8"wil1 again reclose its raise contacts. This will cause the regulator 4 to make a tap change in the voltage raising direction so as to raise the voltage of the load circuit 2 by one-half the tap voltage of the regulators. This will restore theoutput voltages of the regulators to equality so that there will be no voltage tending to cause an exciting current to flow in the winding H.

The same operation in the lowering direction will take place: ii the voltage of circuit 2 rises above normal the regulators operate alternately so as to change the voltage of the circuit-2 in voltage steps which are equal to one-half the tap voltage of the regulators.

through the paralleling connections and consequently the regulators will divide equally as above.

In actual practice, however, it is impossible to,

as the regulator 4 is in its neutral position its impedance is substantially zero so that were it not for the device II the portionof the winding 5' between its output terminal and the next lower- It should be understood that the automatic control means between the auxiliary windings 8 and the tap switches 8. have been shown diagrammatically in their simplest possible form and that in actual practice the regulators will usually be equipped with additional conventional elements such as auxiliary relays between the primary relay and the motor as well as time delay relays between the'auxiliary relays and the motor or between the primary relay and the motor, and that conventional means for driving the tap switches intermittently at a high speed will be interposed between the movable contacts of the tap switches and the operating motors. In many instances line drop compensators will also be in terposed between the auxiliary windings and the primary relays for causing the regulators to hold constant voltage at some relatively remote point on the load circuit. However, these devices play 2,sso,oes

no part in the present invention and so far as the invention is concerned the system operates exactly the same whether or not they are present.

As the regulators will not get more than one step apart, the winding H need not be designed they be single-phase regulators. Thus, in Fig.

2 the invention isshown applied to a pair of dissimilar three-phase regulators indicated schematically as regulator A and regulator B, the former being of smaller size or rating than the latter. These regulators may be of the autotrans-, former type in which case they may consist of three star-connected autotransformer .winding similar to the windings 5 and 5' in Fig. l or they may be of the power or insulating transformer type. As shown, there are as many autotransformers II' as there are phases, the terminals of each autotransformer being connected to corresponding phase output terminals of the regulators and the intermediate points of the windings ii being connected to the corresponding phase conductors of the output circuit 2. The intermediate points on the windings II are so located that when the load currents In and In of the two regulators are in the ratio of the ratings of these regulators the magnetomotive forces of the two parts of the winding II on opposite sides of the intermediate point are equal. In other words, IA times the number of turns between regulator A and the intermediate point equals In times the number of turns between the regulator B and the intermediate point. This means that with the regulators on different voltage steps the voltage of the output circuit will be more nearly the voltage of the larger regulator instead of being the average voltage as in the case of the equal regulators shown in Fig. 1.*

If automatic controls are not used it is not necessary that the autotransformer or trans formers I I be connected between the output terminals of the regulators and they may just as well be connected between the input terminals. Nor is'it necessary that the number of parallel regulators be limited to two. Thus, in Fig. 3 three nonautomatic three-phase regulators A, B and C are paralleled and the inductive devices H, II' and II" consist of sets of as many individual windings as there are regulators, the

sets Ii and Ii' being connected respectively between the input terminals of the X and Y phases of the regulators and the phase conductors X1 and Y1 of the input circuit I while the windings of the set N" are connected respectively between the phase conductor Z: of the output circuit 2 and the output terminals of the Z phases of the three regulators.

The tap-changing or ratio adjusting means of Figs. 1 and 3 have been shown without any conventional means for preventing momentary interruption of the regulator current during a tap-changing operation. It should be understood, however, that in practice conventional load ratio control means, such as by-pass impedances or double-finger switching arrangements would be employed so that the regulator current would not be interrupted during a tap-changing operation.

It should also be understood that the inductive devices H, II' and II'" of Fig. 3 have been shown schematically and that in actual practice they would be rather complicated when more than two regulators are paralleled.

While there have been shown and described particular embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, an alternating-current circuit, a plurality of variable ratio transformers connected in parallel with each other in said circuit, a separate set of windings, the windings of said set being connected respectively between corresponding terminals of said transformers and their corresponding circuit conductor, the windings of said set being closely coupled and having in a common magnetic circuit transformer load current produced magnetomotive forces whose vector sum is zero when the ratio of said load currents is of the order of the ratio of the current ratings of said transformers. I

2. In combination, an altemating-current supply circuit, an alternating-current load circuit, a plurality of variable ratio autotransformer voltage regulators each having a common terminal, an input terminal and an output terminal, means for connecting said input terminals directly to a conductor of said supply circuit, multiwinding inductive means having a neutral point connected to a conductor of said load circuit, said inductive, means having as many free terminals as there are regulators, said free terminals being connected respectively to the output terminals of said regulators. o

3. In combination, an alternating-current power supply circuit, a constant voltage alternating current load circuit, a preventive autotransformer. a pair of step voltage regulators having their primary windings connected in parallel across said supply circuit-and having their secondary windings connected in parallel through said preventive autotransformer across said load circuit, and separate means responsive to the secondary winding voltage of each of said regulators for automatically operating its respective regulator so as to maintain said voltage substantially constant.

4. In combination, an altemating-current power circuit, a pair of automatic single-phase step voltage regulators connected in parallel circuit relation in said circuit, an autotransformer having an intermediate point connected to one of the conductors of said circuit and having its terminals connected respectively to corresponding terminals of said regulators, the ratio of turns of said autotransformer between each terminal thereof and said intermediate point being inversely proportional to the current ratings of the regulators to whose terminals said turns are connected.

5. In combination, polyphase input and output circuits of the same number of corresponding phases, a plurality of polyphase variable ratio transformers having as many input terminals and as many output terminals as said circuits have phases, a plurality of sets of windings, there being as many such sets as said circuits have phases, there being as many windings in each set as there are transformers, a terminal of each winding of one of said sets being connected to one of the phase conductors oi one of said circults vand the remaining terminals thereof being connected respectively to the corresponding termlnals of the regulators, similar connections for each of the other sets of windings and direct connections between the remaining corresponding terminals of the regulators and the remaining conductors of said circuits.

6. In combination, an altemating-current supply circuit, a pair of automatic variable ratio transformers connected to be excited in parallel by said supply circuit, a load circuit, a preventive autotransformer, said load circuit being connected to be energized by said transformers in parallel circuit relation through said preventive transformer, and separate means associated with each transformer and responsive to its output voltage for automatically maintaining said output voltage within predetermined limits by appro- 10 priate control of its transformers voltage ratio.

THOMAS C. LENNOX. 

